1. Field of the Invention
This invention relates generally to a recirculating paint supply system, and more particularly, to a spray nozzle fluid regulator and restrictor combination for use in a recirculating or non-recirculating paint supply system.
2. Discussion of the Related Art
Recirculating paint supply systems conventionally comprise a mixing tank equipped with suitable agitation for maintaining a liquid coating composition uniformly mixed and a pump for transferring the liquid coating composition under a desired pressure through a supply line to a spray gun. Such recirculating type paint systems are in widespread commercial use for keeping heavily-bodied pigments uniformly suspended in the liquid coating composition to thereby assure uniform conformity in the color and quality of the paint layer applied to a surface substrate, such as an automobile. A suitable return hose is also provided for returning the excess quantity of liquid coating composition back to the mixing tank for recirculation and to keep the paint in suspension. A typical recirculating paint supply system is shown in U.S. Pat. No. 5,060,861, which is hereby incorporated by reference.
Some of these paint supply systems will also include a flow control device or paint restrictor at the junction between the supply hose and the spray nozzle of the spray gun. This type of flow control device regulates fluid flow by creating a pressure drop through an orifice in the device. An exemplary embodiment of such a flow control device is set forth in U.S. Pat. No. 4,106,699, which is hereby incorporated by reference. While this type of flow control device works well for maintaining a substantially constant flow rate of the liquid coating composition to the spray nozzle, this type of flow control device also exhibits some disadvantages. For example, should the supply line pressure vary or be pulsating, possibly due to the use of a reciprocating piston type pump, a fluctuation in the flow rate out of the spray nozzle may occur, thereby possibly effecting the quality of the paint finish. In addition, since this type of device does not have a closing valve, pressure may build up between this device and the spray gun. In which case, when the spray gun is actuated, a stream or spit of non-atomized paint may exit the spray gun.
Other paint supply systems may control the fluid pressure in the supply line directly through the use of a diaphragm-type pressure regulator. Such regulators are generally able to compensate for any pulsation due to the modulation of an internal diaphragm. However, due to the corrosive nature of the solvents currently being used in the paint industry, rubber/mylar type diaphragms are no longer an option, which thereby requires that a teflon type diaphragm be used. These diaphragms are generally much stiffer and less responsive than a typical rubber/mylar diaphragm. Because of this, when a spray nozzle is turned off, the diaphragm does not react quickly enough to close the supply to the spray gun, thereby enabling a pressure to build between the regulator and the spray gun. When the spray gun is again actuated, the liquid coating composition exits the spray nozzle at a much higher pressure, sometimes as high as the line pressure, which does not allow the liquid coating composition to become atomized as it initially exits the spray nozzle. This non-atomized paint will again generally effect the overall quality of the paint finish.
Other paint supply systems have also employed the use of a pressure regulator at the bulk head or connection to a spray station, which is generally a very large and expensive regulator and a flow control device at the coupling to the spray gun. Here again, this configuration also has several disadvantages. In this regard, the pressure regulator generally employed is very costly and large. Additionally, with the regulator being adjacent to the bulk head, there is generally a great deal of supply conduit or hose between the regulator and the spray nozzle. Because of this, when the spray gun is turned off, pressure will build between the regulator and the spray nozzle before the regulator fully closes. This will generally cause the volume of paint between the regulator and the spray gun to exit the spray nozzle in a non-atomized state.
What is needed then is a spray nozzle fluid regulator and restrictor combination which does not suffer from the above-mentioned disadvantages. This, in turn, will reduce the cost for providing a constant flow and pressure control, reduce the pressure build-up between the pressure regulator and the spray gun, reduce or eliminate the amount of non-atomized paint exiting the spray nozzle upon initial actuation, provide a substantially uniform flow rate at varying supply line pressures or at pulsating supply line pressures, increase the overall uniformity and quality of paint finishes, and improve the overall performance and responsiveness of the system to control flow rate and spray pressure. It is, therefore, an object of the present invention to provide such a spray nozzle fluid regulator and restrictor combination for use in a recirculating paint supply system.